Information recording method, information recording medium and information recording apparatus

ABSTRACT

An information-recording method and an information-recording medium which make it possible to improve overwrite characteristics in the high speed recording, especially archival overwrite characteristics for overwriting information after retaining the medium in a high temperature environment for a certain period of time, and an information-recording apparatus based on the use of the same are provided. The information-recording method comprises overwriting a random pattern with light beams having a predetermined recording power and a variety of erasing powers; reproducing the random pattern to determine a minimum value Pb 1  and a maximum value Pb 2  of the erasing power obtained when the pattern, in which a reproduction jitter exceeds a predetermined threshold value, is erased; determining an optimum erasing power Pb from the minimum value Pb 1 , the maximum value Pb 2 , and a relational expression represented by Pb=α×Pb 1 +( 1 −α)×Pb 2 ; and recording the information with the determined optimum erasing power Pb. The value of α is previously recorded on the information-recording medium. The information-recording apparatus has a Pb-calculating control unit which reads the value of α when the optimum erasing power Pb is determined.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an information-recording methodand an information-recording medium which make it possible to recordinformation by being irradiated with a laser beam. In particular, thepresent invention relates to an information-recording method, aninformation-recording medium, and an information-recording apparatuswhich are capable of improving overwrite characteristics in the highspeed recording, especially archival overwrite characteristics foroverwriting information after retaining the medium in a high temperatureenvironment for a certain period of time.

[0003] 2. Description of the Related Art

[0004] In recent years, the market of read-only optical disks including,for example, DVD-ROM and DVD-Video is expanded. On the other hand,rewritable DVD's including, for example, DVD-RAM, DVD-RW, and DVD+RW areintroduced into the market, and the market is expanding for backup mediafor computers and image-recording media with which VTR may besubstituted. Further, in these several years, the demand of the markethas increased for the improvement in the access speed and the transferrate of recordable DVD's.

[0005] The phase-change recording system is adopted for recordable DVDmedia such as DVD-RAM and DVD-RW on which information is recordable anderasable. In the case of the phase-change recording system, therecording is basically performed such that pieces of information of “0”and “1” correspond to the crystal and the amorphous. Recorded “0” and“1” can be detected by radiating the laser beam onto the crystallizedportion and the amorphous portion and effecting the reproduction basedon the reflected light beam.

[0006] In order to bring about the amorphous state at a predeterminedposition, the heating is effected so that the temperature of therecording layer is not less than the melting point of the recordinglayer material by radiating a laser beam having a relatively high power.On the other hand, in order to bring about the crystalline state at apredetermined position, the heating is effected so that the temperatureof the recording layer is in the vicinity of the crystallizationtemperature of not more than the melting point of the recording layermaterial by radiating a laser beam having a relatively low power. Bydosing so, it is possible to reversibly change the amorphous state andthe crystalline state. When the overwrite recording is performed on theordinary recordable DVD media, the recording pulse is modulated betweenthe recording laser power and the erasing laser power which is lowerthan the recording laser power to newly perform the recording whileerasing the amorphous marks having been already recorded.

[0007] Optical recording media, which realize satisfactory overwritecharacteristics, are known, including an optical recording medium asdescribed, for example, in Patent Document 1 in which the overwriterecording is performed with such powers that the recording power levelhas a value of not more than an optimum recording power and the erasingpower level has a value higher than an optimum erasing power.

[0008] A drive for the ×2 speed recording (recording speed or velocity:8.2 m/sec, transfer rate: 22 Mbps) for DVD-RAM may be exemplified inrelation to a method for optimizing the erasing power, in which thetrial writing is performed for data by using information on therecording power written on a disk to determine the erasing power. Inthis procedure, the values of the erasing power, which exceed thethreshold value of the error rate on the low power side and the highpower side, are determined to set the optimum erasing power so that theoptimum erasing power is just at the center of the both.

[0009] Patent Document 1Japanese Patent Application Laid-open No.08-007343

SUMMARY OF THE INVENTION

[0010] In order to improve the transfer rate and the access speed on therecordable DVD medium as described above, it is necessary that therecording speed or the recording velocity is increased to perform therecording and the erasing in a short period of time. However, therecording and erasing characteristic, which arises when information isoverwritten on the medium, causes any problem when the high speedrecording is performed. When the high speed recording is performed, thenthe time, which is required for the laser beam to pass over the markposition in the amorphous state subjected to the recording ofinformation, is shortened, and the time, in which the crystallizationtemperature is retained, is shortened as well. If the time, in which thecrystallization temperature is retained, is too short, it is impossibleto effect any sufficient crystal growth. Therefore, in the case of theconventional technique as described above, the overwrite characteristicis deteriorated when the high speed recording is performed. As a resultof further investigations performed by the inventors, it has beenrevealed that the overwrite characteristic is conspicuously deterioratedwhen the medium, on which the high speed recording has been performed,is taken out into an ordinary temperature environment to perform theoverwrite recording after retaining the medium in a high temperatureenvironment for a certain period of time. In the present invention, thecharacteristic, which is obtained when information is overwritten afterretaining the medium in a high temperature environment for a certainperiod of time, is referred to as “archival overwrite characteristic”which is especially distinguished from the ordinary overwritecharacteristic.

[0011] In the technique of Patent Document 1 described above, thedeterioration of the overwrite characteristic, which is caused by anyuneven crystallization when the initialization process is performed at ahigh speed, is improved. The recording speed or velocity, which isobtained in Example, is 7.5 m/sec which is not more than 8.2 m/sec asadopted in the ×2 speed recording on the presently used DVD-RAM. Inparticular, the technique does not provide any countermeasure in whichthe problem involved in the high speed recording exceeding 8.0 m/sec,and especially the problem involved in the archival overwritecharacteristic are taken into consideration. Further, this patentdocument merely describes that the range of the erasing power is higherthan the optimum erasing power and lower than the maximum power at whichthe recording layer is not melted. In the case of this method, it hasbeen revealed that the following problem arises. That is, when the highspeed recording is performed, then the mark is erased due to therecording on the adjoining track, or the leakage of the reproducedsignal from the adjoining track tends to occur.

[0012] Therefore, an object of the present invention is to solve theproblems involved in the conventional technique as described above andprovide an information-recording method, an information-recordingmedium, and an information-recording apparatus which make it possible toimprove overwrite characteristics in the high speed recording,especially archival overwrite characteristics for overwritinginformation after retaining the medium in a high temperature environmentfor a certain period of time.

[0013] According to a first aspect of the present invention, there isprovided an information-recording method for recording information on aninformation-recording medium by radiating a light beam power-modulatedto be at a recording power level and an erasing power level, theinformation-recording method comprising:

[0014] overwriting a random pattern on the information-recording mediumwith light beams having a predetermined recording power and a variety oferasing powers;

[0015] reproducing the overwritten random pattern to determine a minimumvalue Pb1 and a maximum value Pb2 of the erasing power obtained when thepattern, in which a reproduction jitter or a reproduction error exceedsa predetermined threshold value, is erased;

[0016] determining an optimum erasing power Pb for performing therecording from the determined minimum value Pb1, the determined maximumvalue Pb2, and a relational expression represented byPb=α×Pb1+(1−α)×Pb2; and

[0017] recording the information with the determined optimum erasingpower Pb.

[0018] The information-recording medium of the present invention mayfurther comprise determining an optimum recording power Pp by using thedetermined optimum erasing power Pb. A value of α may be previouslyrecorded on the information-recording medium, and the value of a may beread from the information-recording medium when the information isrecorded. Pr<Pb1<Pb and Pb<Pb2<Pp may be satisfied provided that areproducing power is Pr.

[0019] According to a second aspect of the present invention, there isprovided an information-recording medium for recording and reproducinginformation thereon, the information-recording medium comprising:

[0020] an information-recording portion on which the information isrecorded by being irradiated with a light beam having a recording powerPp and an erasing power Pb lower than the recording power Pp and onwhich the information is reproduced by being irradiated with a lightbeam having a reproducing power Pr lower than the erasing power Pb; and

[0021] a control data portion, wherein:

[0022] information for determining an optimum erasing power Pb from aminimum erasing power Pb1 which satisfies Pr<Pb1<Pb and a maximumerasing power Pb2 which satisfies Pb<Pb2<Pp is previously recorded onthe control data portion.

[0023] According to a third aspect of the present invention, there isprovided an information-recording apparatus for recording information onan information-recording medium by radiating a light beampower-modulated to be at a recording power level and an erasing powerlevel, the information-recording apparatus comprising:

[0024] an optical head which radiates the light beam onto theinformation-recording medium;

[0025] a driver which drives the optical head so that the light beam,which is power-modulated to be at the recording power level and theerasing power level, is outputted from the optical head; and

[0026] a Pb-calculating control unit which reproduces a random patternoverwritten with light beams having a predetermined recording power anda variety of erasing powers to determine a minimum value Pb1 and amaximum value Pb2 of the erasing power obtained when the pattern with areproduction jitter or a reproduction error exceeding a predeterminedthreshold value is erased, which reads a coefficient α which is used inan expression Pb=α×Pb1+(1−α)×Pb2 and has been previously recorded on theinformation-recording medium, and which determines an optimum erasingpower Pb to be used when the recording is performed, from the determinedminimum value Pb1, the determined maximum value Pb2, and the readcoefficient α.

[0027] The inventors have made the following consideration about thedeterioration of the archival overwrite characteristic in the high speedrecording in order to improve the problems involved in the conventionaltechnique in the high speed recording. As shown in FIG. 1, the followingfact is appreciated from the positional relationship between positionsof passage of a laser beam and shapes of marks to be recorded on aninformation-recording medium. That is, it is considered that when therecording is performed at a high velocity, the temperature hysteresis,which is caused by the passage of the laser beam, differs between a markarea A disposed in the vicinity of the center of the position of thepassage of the laser beam and a mark area B disposed at a placeseparated from the center of the laser beam.

[0028] At first, the step of recording data will be considered. FIG. 2schematically shows temperature hystereses with respect to the time inthe area A and the area B, obtained when the recording power isradiated. In relation to the temperature hysteresis in the mark area Adisposed in the vicinity of the center of the passage of the laser beam,the temperature is gently lowered from the crystal growth temperature tothe crystal nucleus-generating temperature and to room temperature afterexceeding the melting point. On the other hand, in relation to thetemperature hysteresis in the area B disposed separately from theneighborhood of the center of the passage of the laser beam, it isconsidered that the crystal nuclei-generating time is especiallyshortened as compared with the temperature hysteresis in the area A.When the overwrite recording is performed, then the mark is once erasedby converting the amorphous state into the crystalline state, and thenthe mark is recorded in the amorphous state. In the area B, the numberof crystal nuclei is small in the amorphous state as compared with thearea A. Therefore, it is considered that the erasing, in which the stateis returned to the crystalline state, is not facilitated, and theoverwrite characteristic for the entire mark is consequentlydeteriorated. In other words, it is considered that as the speed is moreincreased, the difference in temperature hysteresis is more increasedbetween the area A and the area B, and the crystal nucleus generation ismore decreased in the area B, especially resulting in the deteriorationof the archival overwrite characteristic in which information isrewritten after retaining the medium in the high temperature environmentfor a certain period of time.

[0029] Next, the step of erasing data will be considered. FIG. 3schematically shows temperature hystereses with respect to the time inthe area A and the area B, obtained when the erasing power is radiated.In relation to the temperature hysteresis in the mark area A disposed inthe vicinity of the center of the passage of the laser beam, thetemperature is gently lowered to room temperature after being retainedat the crystallization temperature for a certain period of time. On theother hand, in relation to the temperature hysteresis in the area Bdisposed separately from the neighborhood of the center of the passageof the laser beam, it is considered that the period of time, in whichthe temperature is retained at the crystallization temperature, is shortas compared with the temperature hysteresis in the area A. As a result,the erasing of date, in which the state is returned from the amorphousstate to the crystalline state, is not performed sufficiently in thearea B as compared with the area A. In particular, it is considered thatthe archival overwrite characteristic is deteriorated for the entiremark when information is overwritten after retaining the medium in thehigh temperature environment for a certain period of time. That is, itis considered that the phenomenon, in which the archival overwritecharacteristic is deteriorated as the recording is performed at thehigher speed, is caused by the decrease in the crystal nucleusgeneration in the data-recording step and the insufficientcrystallization in the erasing step.

[0030] The inventors have completed the information-recording methodaccording to the first aspect of the present invention, theinformation-recording medium according to the second aspect, and theinformation-recording apparatus according to the third aspect on thebasis of the knowledge as described above. When theinformation-recording method, the information-recording medium, and theinformation-recording apparatus of the present invention are used, theerasing laser power level Pb, at which the best archival overwriteperformance is obtained for each of information-recording media, can beset when the trial writing is performed in order to establish the laserpower before recording the information.

[0031] For example, in the case of the information-recording apparatussuch as an optical disk drive, the trial writing is usually performed inorder to determine optimum Pp and Pb before writing information on theoptical disk. In this process, information is recorded with the opticaldisk drive while changing the laser power (overwrite) to measure thenumber of errors for the information written during the recording. Forexample, when the optimum erasing power level Pb is determined, then theminimum erasing power level Pb1 at which the number of errors is notless than a certain reference and the maximum erasing power level Pb2are measured to obtain the intermediate power level Pb therebetween. Theinventors have revealed the fact that the erasing power level, which isdetermined as described above, is not necessarily the optimum powerlevel for the archival overwrite performance. When the relationshipamong Pb1, Pb2, and the optimum erasing power level Pb, especially thecoefficient α in Pb=α×Pb1+(1−α)×Pb2 is previously recorded on theinformation-recording medium, it is possible to provide theinformation-recording medium in which the recording performance is lessdeteriorated even after the storage for a long term. Further, therecording method is provided, in which the value of the coefficient α inPb=α×Pb1+(1−α)×Pb2 is read from the information-recording medium asdescribed above to determine the optimum erasing power level Pb, and therecording is successfully performed by using the erasing power level Pbpreferred for each of the recording speeds. The physical meaning of Pb1is the laser power level at which the change is started from thecrystalline state to the amorphous state, and Pb2 is the laser powerlevel at which the change is started from the amorphous state to thecrystalline state. Pb1 and Pb2 may be defined, for example, by the powerlevel in which the jitter level of the reproduced signal is used as thethreshold value. Alternatively, as described above, Pb1 and Pb2 may bedefined by using the number of errors of information as the thresholdvalue. In any case, the information, which is reproduced from theinformation-recording medium on which the value of a is recorded, can beused to set the erasing laser power level Pb at which the archivaloverwrite characteristic is optimized, by using the values of Pb1 andPb2. Thus, it is possible to improve the archival overwritecharacteristic.

[0032] As for the information-recording medium of the present invention,when the information-recording medium, on which the information inrelation to the relationship among Pb, Pb1, and Pb2 is recorded togetherwith information in relation to a recording velocity, is used, it ispossible to set the erasing power at which the archival overwritecharacteristic is optimized depending on each of the recordingvelocities when the recording velocity is changed for each of recordingradiuses as in the information-recording apparatus based on the CAV(Constant Angular Velocity) system. Thus, it is possible to improve thearchival overwrite characteristic.

[0033] As for the information-recording medium of the present invention,the information, which relates to the relationship among Pb, Pb1, andPb2, may be defined by Pb=α×Pb1+(1−α)×Pb2 by using the ratio a betweenPb1 and Pb2. When this information-recording medium is used, it ispossible to set the optimum erasing power at which the archivaloverwrite characteristic is optimized for each of the recordingvelocities on the basis of the margin curve of the erasing power to beused when the erasing power is optimized with the drive for the ×2 speedrecording (recording velocity: 8.2 m/sec, transfer rate: 22 Mbps) forDVD-RAM commercially available at present. The dispersion of thearchival overwrite characteristic, which would be otherwise causeddepending on the recording velocity, disappears. In particular, it isunnecessary to perform any complicated design change of the drive aswell. Thus, it is possible to guarantee the downward compatibility forthe drive when the recording velocity is quickened.

[0034] As for the information-recording medium of the present invention,on condition that the value of α satisfies α≦0.50, when the value of theerasing power Pb is set to be a value of not less than0.50×Pb1+0.50×Pb2, then the laser energy is enhanced upon the erasingduring the high speed overwrite, and the period of time, in which thetemperature is retained at a temperature of not less than thecrystallization temperature, is relatively prolonged. Further, when theerasing of data is sufficiently performed to make the return from theamorphous state to the crystalline state, it is possible to improve thearchival overwrite characteristic during the high speed recording. Inparticular, on condition that the value of a satisfies 0.25≦α≦0.50, whenthe value of Pb is set to be not less than 0.50×Pb1+0.50×Pb2 and notmore than 0.25×Pb1+0.75×Pb2, it is possible to suppress the erasing ofthe mark signal on the adjoining track, which would be otherwise causedby the increase in the size of the recording mark. Further, when therecording is performed with any different information-recordingapparatus, the cross power overwrite characteristic, which is theoverwrite characteristic assuming that the recording power differs, canbe also retained to have a satisfactory value. The cross power overwritecharacteristic herein refers to the characteristic to be obtained whenthe overwrite recording is performed at a recording power of 90% afterperforming the recording at a power of 105% on condition that theoptimum recording power is 100%.

[0035] When the information-recording medium of the present invention isused, it is possible to perform the high speed recording, in which therecording linear velocity is not less than 9 m/sec. Further, thegeneration of crystal nuclei during the recording of data and theretention of the crystallizing time during the erasing of data arefacilitated. Thus, it is possible to improve the archival overwritecharacteristic during the high velocity recording.

[0036] When the information-recording apparatus, in which information isrecorded by using the information-recording medium of the presentinvention, is used, the following advantage is obtained when therecording is performed by using a plurality of information-recordingapparatuses having different recording velocities by using the identicalinformation-recording medium. That is, the information on the recordingvelocity and the erasing power, which is previously written on theinformation-recording medium, is read by the information-recordingapparatus to record information, and thus the recording compatibilitycan be obtained for the information-recording apparatuses.

[0037] When the information-recording method and theinformation-recording medium of the present invention are used, then therecording can be performed with the erasing power which is optimizeddepending on the recording speed, and the archival overwritecharacteristic is optimized. The information-recording apparatus of thepresent invention makes it possible to read the information in relationto the optimized erasing power from the information-recording medium andexecute the recording with the optimized erasing power.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 schematically shows positions of passage of a laser beamand shapes of marks to be recorded on a medium.

[0039]FIG. 2 schematically shows temperature hystereses with respect tothe time in an area A and an area B obtained when a recording power isradiated.

[0040]FIG. 3 schematically shows temperature hystereses with respect tothe time in the area A and the area B obtained when an erasing power isradiated.

[0041]FIG. 4 schematically shows a recording and reproducing apparatusequipped with an information-recording medium used to investigaterecording and reproduction characteristics in the embodiments of thepresent invention.

[0042]FIG. 5 explains the strategy for the recording pulse used toinvestigate recording and reproduction characteristics in theembodiments of the present invention.

[0043]FIG. 6 schematically shows the dependency of the jitter on theerasing power to illustrate the definition of the erasing power used inthe embodiments of the present invention.

[0044]FIG. 7 schematically shows the dependency of the jitter on therecording power to illustrate the definition of the recording power usedin the embodiments of the present invention.

[0045]FIG. 8 schematically shows an information-recording portion and acontrol data portion on an information-recording medium according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Embodiments of the present invention will be explained below onthe basis of results of experiments performed by the inventors.

[0047] An information-recording medium was obtained as follows. That is,films were successively formed with the sputtering process on apolycarbonate substrate having a radius of 120 mm and a thickness of 0.6mm with a surface covered with concave/convex guide grooves having atrack pitch of 1.2 μm and a groove depth of 63 nm on the basis of theformat for 4.7 GB DVD-RAM such that ZnS—SiO₂ was formed as a firstprotective layer to have a thickness of 100 nm, GeCrN was formed as afirst interface layer to have a thickness of 10 nm, BiGeTe was formed asa recording layer to have a thickness of 10 nm, GeCrN was formed as asecond interface layer to have a thickness of 10 nm, ZnS—SiO₂ was formedas a second protective layer to have a thickness of 50 nm, GeCr wasformed as a heat absorption factor-correcting layer to have a thicknessof 50 nm, and Al was formed as a heat-diffusing layer to have athickness of 120 nm. Thus, the information-recording medium used in theembodiment was obtained.

[0048] When the recording and reproduction characteristics wereinvestigated after crystallizing the information-recording medium byusing a laser initializing apparatus, an information-recording andreproducing apparatus equipped with an optical recording medium shown inFIG. 4 was used.

[0049] An explanation will be made below about the recording andreproduction process and the operation of the information-recording andreproducing apparatus equipped with the optical recording medium used inthe embodiment of the present invention. At first, the information,which is supplied from the outside of the recording apparatus, istransmitted to an 8-16 modulator 47 while one unit comprises 8 bits.When the information is recorded on the information-recording medium 41,the modulation system in which 8-bit information is converted into16-bit information, i.e., the so-called 8-16 modulation system is used.In this modulation system, the information composed of mark lengths of 3T to 14 T, which corresponds to the 8-bit information, is recorded onthe information-recording medium. The 8-16 modulator 47 shown in FIG. 4performs this modulation. “T” herein means the data clock length uponthe information recording. In this embodiment, T was 17.1 ns when therecording linear velocity was 8.2 m/sec, T was 8.6 ns when the recordinglinear velocity was 16.4 m/sec, and T was 5.7 ns when the recordinglinear velocity was 24.6 m/sec.

[0050] The digital signals of 3 T to 14 T converted by the 8-16modulator 47 are transmitted to a recording waveform-generating circuit45. Assuming that the width of the pulse of the power at the first powerlevel Pp as the recording power is about T/2, the laser is radiated atthe first power level Pp and the second power level Pb as the erasingpower with the width of about T/2 in the radiation time for the laser ofPp to generate a multi-pulse recording waveform in which the laser isradiated at the power level Pb between the series of pulses at the Pplevel. In the recording waveform-generating circuit 45, the signals of 3T to 14 T alternately correspond to “0” and “1” in time series. In thecase of “0”, the laser power at the power level of Pb is radiated, andin the case of “1”, the laser power at the power level of Pp isradiated. In this procedure, the portion on the information-recordingmedium 41, which is irradiated with the laser beam at the power level ofPb, is changed into the crystal, and the portion, which is irradiatedwith the series of pulse sequence including pulses at the power level ofPb, is changed into the amorphous (mark portion). The recordingwaveform-generating circuit 45 has a multi-pulse waveform tablecorresponding to the system (adaptive recording waveform control) inwhich the leading pulse width Tfp and the trailing pulse width Tlp ofthe multi-pulse waveform as shown in FIG. 5 are changed depending on thespace lengths before and after the mark portion when the series of pulsesequence including the pulse at the power level of Pb for forming themark portion is formed. Thus, the recording waveform-generating circuit45 generates the multi-pulse recording waveform which makes it possibleto maximally exclude the influence of the thermal interference betweenthe marks generated between the marks.

[0051] The recording waveform, which is generated by thewaveform-generating circuit 45, is transmitted to the laser-drivingcircuit (driver) 46. The laser-driving circuit 46 controls asemiconductor laser included in an optical head 43 to emit light on thebasis of the recording waveform. The semiconductor laser having awavelength of 655 nm is used as the laser beam for recording informationin the optical head 43 which is carried on the information-recording andreproducing apparatus equipped with the optical recording medium of thepresent invention. The laser beam is focused onto the recording layer ofthe information-recording medium 41 with an objective lens having NA of0.6. The laser beam of the laser corresponding to the recording waveformis radiated to perform the recording.

[0052] The information-recording and reproducing apparatus equipped withthe optical recording medium of the present invention is adapted to therecording system (so-called the land-groove system) in which informationis recorded on both of the groove and the land (area between thegrooves). In the information-recording and reproducing apparatusequipped with the optical recording medium of the present invention, anL/G serve circuit 48 can be used to arbitrarily select the tracking forthe land and the groove. The recorded information was reproduced byusing the optical head 43 as well. A reproduced signal is obtained byradiating the laser beam onto the recorded marks and detecting thereflected light beam from the marks and the portions other than themarks. The amplitude of the reproduced signal is increased by using apreamplifier circuit 44, followed by being transferred to an 8-16demodulator 49. The 8-16 demodulator makes the conversion into 8-bitinformation for every 16 bits. As a result of the operation as describedabove, the reproduction from the recorded marks is completed. When therecording is performed on the optical information-recording medium 41under the condition as described above, then the mark length of the 3Tmark as the shortest mark is about 0.42 μm, and the mark length of the14 T mark as the longest mark is about 1.96 μm.

[0053] When the jitter was evaluated, a random pattern signal including3 T to 14 T was subjected to the recording and reproduction. An obtainedreproduced signal was subjected to the processes of the waveformequivalence, the conversion into the binary system, and PLL (PhaseLocked Loop) to measure the jitter. When the signal was reproduced, thelinear velocity was constant at 8.2 m/sec irrelevant to the recordingvelocity.

[0054] The archival overwrite jitter, the cross power overwrite jitter,and the cross erase jitter were measured as described below in relationto the characteristic evaluation.

[0055] At first, as for the archival overwrite jitter, the randompattern was recorded ten times on the track. After that, an accelerationtest was performed with the storage in an environment of 90° C. and 30%R.H. for 20 hours, and then the temperature was returned to roomtemperature to overwrite the random pattern. The reproducing laser powerPr was set to 1.0 mW to measure the jitter. As a result ofinvestigations performed by the inventors, the increase in the archivaloverwrite jitter is approximately saturated by the storage in theenvironment of 90° C. and 30% R.H. for 20 hours. Therefore, it isconsidered that the overwrite characteristic corresponding to 10 yearsat room temperature can be guaranteed if the characteristic can beguaranteed in the environment described above. In the embodiment of thepresent invention, the target value of the jitter is set to be not morethan 10% and the normalized upper limit value is set to be not more than11% for the archival overwrite jitter when the recording is performed atlinear velocities of 8.2 to 24.6 m/sec as the ×2 to ×6 speed recordingoperations with clock lengths of 17.1 to 5.7 ns and data transfer ratesof 22 to 66 Mbps. The normalized upper limit value herein refers to theupper limit value of the characteristic at which the medium can beactually used in the drive without any problem.

[0056] As for the cross power overwrite jitter, the random pattern wasrecorded ten times on the track with the optimum laser power. Afterthat, the overwrite was made once with a power which was 105% of theoptimum laser power, and the overwrite was made once thereon with apower which was 90% of the optimum laser power. The reproducing laserpower Pr was set to 1.0 mW to measure the jitter. The cross poweroverwrite jitter is the characteristic to guarantee the reliability ofdata when the overwrite recording is performed in different drives atdifferent recording powers, i.e., the characteristic to represent therecording compatibility of the drive. In the embodiment of the presentinvention, the target value of the jitter is set to be not more than11%, and the normalized upper limit value is set to be not more than 12%for the cross power overwrite jitter.

[0057] As for the cross erase jitter, the random pattern was recordedten times on the middle track, and then the random pattern was recordedten times from the inner circumference to the outer circumference on thetracks disposed on both sides thereof and further on the track disposedon both sides thereof in this order. After that, the reproducing laserpower Pr was set to 1.0 mW to measure the jitter value on the centraltrack of the five tracks. The cross erase jitter is the characteristicto represent the erasing of the mark due to the recording on theadjoining track and the leakage of the reproduced signal from theadjoining track. In the embodiment of the present invention, the targetvalue of the jitter was set to be not more than 8%, and the normalizedupper limit value is set to be not more than 9% for the cross erasejitter.

[0058] An explanation will be made below about the procedure toinvestigate the value of the jitter by recording and reproducing datawhile changing the construction of the recording pulse sequence(recording strategy) and the linear velocity by using the apparatus forevaluating the optical recording medium as described above. In thisembodiment, the linear velocity of the recording is set to 8.2 m/sec,the clock length of the recording data is set to 17.1 ns, and the datatransfer rate is set to 22 Mbps for the ×2 speed recording. For the ×4speed recording, the linear velocity of the recording is set to 16.4m/sec, the clock length of the recording data is set to 8.6 ns, and thedata transfer rate is set to 44 Mbps. For the ×6 speed recording, thelinear velocity of the recording is set to 24.6 m/sec, the clock lengthof the recording data is set to 5.7 ns, and the data transfer rate isset to 66 Mbps.

[0059] The recording strategy at each of the recording velocities, therecording power Pp, and the erasing power Pb were determined as follows.

[0060] At first, temporary laser powers were set to Pp0=10.5 mW andPb0=4.0 mW in the ×2 speed recording, Pp0=13.0 mW and Pb0=5.0 mW in the×4 speed recording, and Pp0=14.0 mW and Pb0=5.5 mW in the ×6 speedrecording. At each of the recording velocities, the temporary laserpower was used to record the marks of 3 T to 14 T. The leading pulsewidth Tfp and the trailing pulse width Tlp before and after each of the3 T to 14 T marks were determined as illustrated in the recordingwaveform shown in FIG. 5 so that the thermal interference between themarks generated between the marks was minimized, which was used as therecording strategy. In this process, the width Tmp of the multi-pulsewas a half of the clock length at each of the recording velocities.

[0061] Subsequently, the recording power was set to the temporaryrecording power Pp0 by using the recording strategy as described aboveat each of the recording velocities, and the erasing power Pb was set tovalues at 0.2 mW intervals from 2.0 mW to 8.0 mW. The random pattern wasrecorded ten times. After that, the reproducing laser power Pr was setto 1.0 mW to measure the jitter. Thus, the dependency of the jitter onthe erasing power was investigated as shown in FIG. 6. The followingmethod was used to determine the erasing power Pb to be used when thedata was actually recorded. That is, the lower erasing power wasdesignated as Pb1, and the higher erasing power was designated as Pb2,which were the erasing powers at which the jitter was 13% in thedependency of the jitter on the erasing power as shown in FIG. 6. Inthis investigation, Pb1=2.5 mW and Pb2=6.1 mW were given in the ×2 speedrecording, Pb1=3.5 mW and Pb2=6.8 mW were given in the ×4 speedrecording, and Pb1=4.3 mW and Pb2=7.4 mW were given in the ×6 speedrecording. Further, the following fact was revealed. That is, the shapeof the curve obtained in this case by plotting the jitter with respectto the recording power at each of the recording velocities was not onlyshifted due to the difference in power levels of Pb1 and Pb2, but thepower range was also obtained, in which the jitter was low and stablewith the low jitter power range which resided in the central value ofPb1-Pb2 at the ×2 speed, while the curve was shifted toward the highpower side from the central value of Pb1-Pb2 when the recording velocitywas high. According to this fact, it is affirmed that the minimum jitteris not necessarily obtained depending on the recording speed or velocityby merely setting Pb to (Pb1−Pb2)/2.

[0062] The following method was used to determine the erasing power Pbto be used when the data was recorded at each of the recordingvelocities. That is, the ratio between Pb1 and Pb2 was used to make thesetting as Pb=α×Pb1+(1−α)×Pb2, and the value of Pb was determined at theerasing power as described above while changing the value of α tosatisfy α=0.2 to 0.6.

[0063] The recording power was set at intervals of 0.5 mW from 8.0 mW to16.0 mW by using the recording strategy as described above for each ofthe determined values of Pb. The random pattern was recorded ten times.After that, the reproducing laser power Pr was set to 1.0 mW to measurethe jitter, and the dependency of the jitter on the recording power wasinvestigated as shown in FIG. 7. In the dependency of the jitter on therecording power shown in FIG. 7, the optimum recording power Pp wasdetermined with Pp=K×Pb1 as the function of Pp1 with respect to therecording power Pp1 at which the jitter was 13%. In this process, theoptimum recording power resided in K=1.25 in the ×2 speed recording,K=1.30 in the ×4 speed recording, and K=1.30 in the ×6 speed recording.

[0064] The recording strategy, the recording power Pp, and the erasingpower Pb determined as described above were used to measure the archivaloverwrite jitter, the cross power overwrite jitter, and the cross erasejitter as the qualities of the recording signal in relation to therespective recording velocities on the land. The relationship betweenthe quality of the recording signal and the value of α when the erasingpower Pb was determined was investigated.

EXAMPLE 1

[0065] The value of a was changed to 0.60, 0.50, 0.40, 0.35, 0.30, 0.25,and 0.20 at a linear velocity of 8.2 m/sec as the ×2 speed recording todetermine recording powers at the respective erasing powers. After that,the archival overwrite jitter, the cross power overwrite jitter, and thecross erase jitter were investigated at the respective values of α.Obtained results are shown in Table 1. TABLE 1 α 0.60 0.50 0.40 0.350.30 0.25 0.20 Recording 11.0 10.7 10.6 10.5 10.4 10.3 10.2 power Pp(mW) Erasing 3.9 4.3 4.7 4.8 5.0 5.2 5.4 power Pb (mW) Archival 8.5 8.38.3 8.4 8.4 8.5 8.8 overwrite jitter (%) Cross power 11.0 10.8 10.8 10.911.6 12.4 13.1 overwrite jitter (%) Cross erase 8.2 8.0 8.3 9.1 9.6 10.110.7 jitter (%)

[0066] When the ×2 speed recording is performed at the linear velocityof 8.2 m/sec, then the archival overwrite jitter is approximatelyconstant within a range of α=0.60 to 0.25, and the jitter is slightlydeteriorated when the value of a is smaller than the value describedabove. On the other hand, such a tendency is observed that the crosspower overwrite jitter is approximately constant within a range ofα=0.60 to 0.35, and the jitter is deteriorated when the value of a issmaller than the above. Further, the cross erase jitter is approximatelyconstant within a range of α=0.60 to 0.40, and the jitter isdeteriorated when the value of α is smaller than the above.

[0067] When the target value of the archival overwrite jitter is 10%,the target value of the cross power overwrite jitter is 11%, and thetarget value of the cross erase jitter is 8%, then the target values areachieved at α=0.50 in the case of the ×2 speed recording at the linearvelocity of 8.2 m/sec. When the normalized upper limit value of thearchival overwrite jitter is 11%, the normalized upper limit value ofthe cross power overwrite jitter is 12%, and the normalized upper limitvalue of the cross erase jitter is 9% as the allowable limits of thecharacteristics, then the normalized values are satisfied within a rangeof α=0.60 to 0.40 in the case of the ×2 speed recording at the linearvelocity of 8.2 m/sec. However, taking the margins of the respectivecharacteristics into consideration, the following fact is affirmed. Thatis, it is most preferable to set to α=0.50 in the case of the ×2 speedrecording at the linear velocity of 8.2 m/sec.

EXAMPLE 2

[0068] The value of a was changed to 0.60, 0.50, 0.40, 0.35, 0.30, 0.25,and 0.20 at a linear velocity of 16.4 m/sec as the ×4 speed recording todetermine recording powers at the respective erasing powers. After that,the archival overwrite jitter, the cross power overwrite jitter, and thecross erase jitter were investigated at the respective values of α.Obtained results are shown in Table 2. TABLE 2 α 0.60 0.50 0.40 0.350.30 0.25 0.20 Recording 11.6 11.4 11.2 11.1 11.0 10.9 10.8 power Pp(mW) Erasing 4.8 5.2 5.5 5.6 5.8 6.0 6.1 power Pb (mW) Archival 11.510.3 9.6 9.4 9.5 9.6 9.8 overwrite jitter (%) Cross power 12.1 11.5 11.010.9 11.1 11.7 12.5 overwrite jitter (%) Cross erase 7.6 7.6 7.6 7.8 7.87.8 8.3 jitter (%)

[0069] When the ×4 speed recording is performed at the linear velocityof 16.4 m/sec, then the archival overwrite jitter is approximatelyconstant within a range of α=0.40 to 0.20, and the jitter isdeteriorated when the value of a is larger than the above. On the otherhand, such a tendency is observed that the cross power overwrite jitteris approximately constant within a range of α=0.40 to 0.30, and thejitter is deteriorated when the value of α is smaller or larger than theabove. Such a tendency is observed that the cross erase jitter isapproximately constant within a range of α=0.60 to 0.25, and the jitteris deteriorated when the value of a is smaller than the above.

[0070] In the case of the ×4 speed recording at the linear velocity of16.4 m/sec, the target values are satisfied within a range of α=0.40 to0.35. Further, the normalized upper limit values are satisfied within arange of α=0.50 to 0.25. Considering the fact that the archivaloverwrite jitter and the cross erase jitter are minimized within therange as described above, the following fact is affirmed. That is, inthe case of the ×4 speed recording at the linear velocity of 16.4 m/sec,it is most preferable to set to α=0.35.

[0071] As compared with the recording at the linear velocity of 8.2m/sec in Example 1, in the case of the higher speed recording at thelinear velocity of 16.4 m/sec, the archival overwrite jitter is clearlyimproved when the value of a is smaller than 0.5. In particular, as forthe archival overwrite jitter, the optimum value of α is not onlyshifted to the smaller range, but the range of α itself is also narrowedto about a half of that obtained in the ×2 speed recording. It is moreimportant to set the optimum recording strategy.

EXAMPLE 3

[0072] The value of a was changed to 0.60, 0.50, 0.40, 0.35, 0.30, 0.25,and 0.20 at a linear velocity of 24.6 m/sec as the ×6 speed recording todetermine recording powers at the respective erasing powers. After that,the archival overwrite jitter, the cross power overwrite jitter, and thecross erase jitter were investigated at the respective values of α.Obtained results are shown in Table 3. TABLE 3 α 0.60 0.50 0.40 0.350.30 0.25 0.20 Recording 14.4 14.3 14.1 14.0 13.9 13.8 13.7 power Pp(mW) Erasing 5.5 5.9 6.2 6.3 6.5 6.6 6.8 power Pb (mW) Archival 12.311.2 10.4 9.9 9.8 10.0 10.5 overwrite jitter (%) Cross power 12.5 12.111.5 11.0 10.8 11.0 11.1 overwrite jitter (%) Cross erase 8.0 7.9 7.97.8 7.9 8.1 8.6 jitter (%)

[0073] When the ×6 speed recording is performed at the linear velocityof 24.6 m/sec, then the archival overwrite jitter is approximatelyconstant within a range of α=0.35 to 0.25, and the jitter isdeteriorated when the value of a is larger than the above. On the otherhand, such a tendency is observed that the cross power overwrite jitteris approximately constant within a range of α=0.35 to 0.20, and thejitter is deteriorated when the value of α is larger than the valuedescribed above. Such a tendency is observed that the cross erase jitteris approximately constant within a range of α=0.60 to 0.25, and thejitter is deteriorated when the value of α is smaller than the above.

[0074] In the case of the ×6 speed recording at the linear velocity of24.6 m/sec, the target values are satisfied within a range of α=0.35 to0.25. Further, the normalized upper limit values are satisfied within arange of α=0.40 to 0.20. Considering the fact that the archivaloverwrite jitter and the cross erase jitter are minimized within therange as described above, the following fact is affirmed. That is, inthe case of the ×6 speed recording at the linear velocity of 24.6 m/sec,it is most preferable to set to α=0.30. As compared with the recordingat the linear velocity of 8.2 m/sec in Example 1 and the high speedrecording at the linear velocity of 16.4 m/sec in Example 2, in the caseof the higher speed recording at the linear velocity of 24.6 m/sec inExample 3, the archival overwrite jitter is clearly improved when thevalue of a is decreased. Further, the optimum value of α is not onlyshifted to the smaller range as compared with the ×4 speed recording,but the range of α itself is also narrowed to about a half of thatobtained in the ×4 speed recording. It is more important to set theoptimum recording strategy.

[0075] The results of Examples 1, 2, and 3 described above aresummarized as follows. The erasing power level Pb is defined to bePb=α×Pb1+(1−α)×Pb2 by using the value Pb1 which is larger than thereproducing power Pr and smaller than Pb and the value Pb2 which islarger than Pb and smaller than the recording power Pp. On thisdefinition, the value of α is given as follows, which is most preferredto improve the archival overwrite jitter, the cross power overwritejitter, and the cross erase jitter. That is, α=0.50 is given when therecording is performed at the linear velocity of 8.2 m/sec, α=0.35 isgiven when the recording is performed at the linear velocity of 16.4m/sec, and α=0.30 is given when the recording is performed at the linearvelocity of 24.6 m/sec.

[0076] The optimum ranges of a in Examples 1, 2, and 3 are compared witheach other as shown in Table 4. Both of the value and the range of αcorresponding to the recording speed greatly differ in relation to thearchival overwrite jitter and the cross power overwrite jitter with goodresults for all of the characteristics including the cross erase jitter.Further, no α exists, which is capable of covering all of the recordingvelocities. Therefore, it is necessary that α is set depending on therecording velocity, and it is necessary to set the recording power Ppand the erasing power Pb. TABLE 4 α 0.6 0.5 0.4 0.3 0.2 Archivaloverwrite jitter x2 x4 x6

Cross power overwrite jitter x2 x4 x6

Cross erase jitter x2 x4 x6

[0077] The reason, why the optimum α differs depending on the linearvelocity of the recording as described above, is considered to be asfollows. As the recording speed is increased, the crystal nucleusgeneration is decreased in the recording process, and thecrystallization is insufficient in the erasing process. As a result, thearchival overwrite characteristic is deteriorated. On the contrary, itis considered that the crystal nucleus generation in the recordingprocess and the crystallization in the erasing process are facilitatedby performing the recording at the optimum erasing power by changing thedefinition of the erasing power determined from the dependency of theerasing power on the jitter in accordance with the linear velocity ofthe recording.

[0078] However, when the erasing power is increased, the archivaloverwrite jitter, the cross power overwrite jitter, and the cross erasejitter are deteriorated. Therefore, the setting of the appropriateerasing power at each recording velocity, i.e., the appropriate value ofα exists. In other words, when the information in relation to therelationship among Pb1, Pb2, and Pb is previously recorded on themedium, then the recording can be performed at the preferred erasingpower, and it is possible to improve the archival overwrite jitter.Further, when the information in relation to α to represent the value ofPb with the ratio between the value of Pb1 and the value of Pb2 ispreviously recorded on the medium, then the recording can be performedat the appropriate erasing power at each linear velocity, and it ispossible to improve the archival overwrite jitter, the cross poweroverwrite jitter, and the cross erase jitter.

[0079] As explained above, it is possible to improve the overwritecharacteristics when the high speed recording is performed, especiallythe archival overwrite characteristics for overwriting information afterretaining the medium in a high temperature environment for a certainperiod of time by using the information-recording medium on whichinformation is recorded by relatively scanning the information-recordingmedium across a laser beam at a linear velocity within a certain range,and power-modulating a laser power of the laser beam to obtain at leasta recording laser power Pp and an erasing laser power level Pb lowerthan a recording laser power level to change a state of aninformation-recording portion of the information-recording medium, andthe information is reproduced with a laser beam at a reproducing laserpower level Pr which is lower than the erasing laser power level Pb,wherein information in relation to a relationship among a value Pb1which is larger than Pr and smaller than Pb, a value Pb2 which is largerthan Pb and smaller than Pp, and Pb is recorded.

EXAMPLE 4

[0080] In this embodiment, the information-recording medium, on whichthe preferred value of α obtained in the foregoing embodiment had beenpreviously recorded, was subjected to the reproduction with theinformation-recording and reproducing apparatus, and the data was readand written by using the value of α to investigate the archivaloverwrite characteristic.

[0081] Stampers were manufactured in order to produce disks each ofwhich had the format of 4.7 GB DVD-RAM and each of which was writtenwith information on α, the sensitivity coefficient of recording, andinformation on the recording strategy for each of the ×5 speed recordingand the ×6 speed recording on the control data portion in the samemanner as in the ×2 speed recording. In this case, two types of thestampers were manufactured, i.e., Stamper A in which the values of α forthe ×5 speed recording and the ×6 speed recording satisfied α=0.50 andα=0.50 respectively and Stamper B in which the values of α for the ×5speed recording and the ×6 speed recording satisfied α=0.40 and α=0.35respectively. In this case, α is the coefficient to determine theerasing power Pb from the relational expressions of Pb=α×Pb1+(1−α)×Pb2,Pb1<Pb2.

[0082] Polycarbonate substrates A and B were formed by the injectionmolding by using Stamper A and Stamper B. Films were successively formedby the sputtering on each of the obtained substrates such that ZnS—SiO₂was formed to have a thickness of 100 nm as a first protective layer,GeCrN was formed to have a thickness of 10 nm as a first interfacelayer, BiGeTe was formed to have a thickness of 10 nm as a recordinglayer, GeGrN was formed to have a thickness of 10 nm as a secondinterface layer, ZnS—SiO₂ was formed to have a thickness of 50 nm as asecond protective layer, GeCr was formed to have a thickness of 50 nm asa heat absorption factor-correcting layer, and Al was formed to have athickness of 120 nm as a heat-diffusing layer to obtain theinformation-recording medium. FIG. 8 schematically shows aninformation-recording portion 75 and a control data portion 71 of theobtained information-recording medium 1. The information-recordingmedium was initialized to prepare Disk A and Disk B. Manufactured Disk Aand Disk B were used to perform the ×5 speed recording and the ×6 speedrecording with the drive.

[0083] An explanation will now be made about the recording andreproducing apparatus (drive unit) used herein to perform the ×5 speedrecording and the ×6 speed recording. (1) At first, the apparatus readsthe information on the recording power for the trial writing and therecording strategy for each of the speeds written on the control dataportion. (2) Subsequently, the erasing power is changed by using therecording power and the recording waveform of the recording strategywhich has been read, to record the random pattern in order to determinethe erasing powers Pb1, Pb2 (Pb1<Pb2) at which the error exceeds thethreshold value. In this procedure, the threshold value of the error isdistinguished with the power at which the number of errors aftercorrecting errors is suddenly changed from several hundreds to severalones. (3) The values of Pb1, Pb2 are used to determine the value of theerasing power Pb optimum for actually performing the recording accordingto the expression of Pb=α×Pb1+(1−α)×Pb2. (4) The determined value of theoptimum erasing power Pb is used to record the 6 T pattern whilechanging the recording power to determine the recording compensationpower at which the value of asymmetry of the 6 T pattern written on thecontrol data portion is obtained. (5) The recording compensation powerand the optimum erasing power are used to optimize the recordingstrategy. In this procedure, the recording strategy is optimized so thatthe error rate is minimized by changing the leading pulse width Tfp andthe trailing pulse width Tlp of the multipulse waveform depending on thespace lengths before and after the mark portion. (6) The optimizedwaveform of the recording strategy and the erasing power Pb are used torecord the random pattern while changing the recording power todetermine the recording power at which the error exceeds the thresholdvalue. (7) Subsequently, the information on the sensitivity coefficientof the recording power written on the control data portion is read, andthe determined recording power is multiplied by the sensitivitycoefficient to obtain the optimum recording power. (8) The steps of (1)to (7) described above are performed for the ×5 speed recording and the×6 speed recording respectively to determine the optimum strategy, theoptimum recording power, and the optimum erasing power which are used torecord the data with the recording and reproducing apparatus.

[0084]FIG. 4 schematically shows the recording and reproducingapparatus. The coefficient α of the erasing power, which is recorded onthe disk, is read to calculate the erasing power Pb according to therelational expression of Pb=α×Pb1+(1−α)×Pb2. This calculation isperformed by a Pb-calculating control unit 410. Theinformation-recording and reproducing apparatus of the present inventionhas principally the same structure as the conventional recordingapparatus (drive unit) for the ×2 speed recording or the ×3 speedrecording except that the Pb-calculating control unit 410 is provided.

[0085] Next, a description will be made about a procedure to investigatethe archival overwrite characteristic during the ×5 speed recording andthe ×6 speed recording with the drive with Disk A and Disk B. At first,the random data is written ten times with the determined optimum power.The disk, on which the recording has been completed, is stored for 20hours in an environment of 90° C. and 30% R.H., and then the disk isreturned to room temperature to write the random data once at the sameposition. After that, the disk, on which the recording has beencompleted, is subjected to the ×2 speed reproduction of the recordeddata with the reproducing power Pr=1 mW by using theinformation-recording and reproducing apparatus equipped with theoptical recording medium as described above to investigate the archivaloverwrite jitter after the environmental test.

[0086] The following radial positions were used to perform the recordingon the disk with the drive. That is, the recording was performed atpositions of radiuses from 43.30 mm to 44.20 mm for the ×5 speedrecording, and the recording was performed at positions of radiuses from45.23 mm to 46.13 mm for the ×6 speed recording. When the jitter wasinvestigated after the environmental test, then the reproduction jitterwas investigated for every 5 tracks for the recording area, and anobtained average value was regarded as the archival overwrite jitterafter the environmental test.

[0087] When the random data was written once with the drive after theenvironmental test, the drive was used to again perform the steps ofdetermining the optimum strategy, the optimum recording power, and theoptimum erasing power as described above. The optimum strategy, theoptimum recording power, and the optimum erasing power, which weredetermined before and after the environmental test, were not changed.

[0088] Table 5 shows results of the investigation on the archivaloverwrite characteristics upon the ×5 speed recording and the ×6 speedrecording with the drive by using Disk A and Disk B described above.TABLE 5 Preset Archival value of α overwrite jitter x5 speed x6 speed x5speed x6 speed recording recording recording recording Disk A α = 0.50 α= 0.50 11.5% 12.7% Disk B α = 0.40 α = 0.35 10.1% 10.8%

[0089] As appreciated from the results shown in Table 5 as well, whenthe high speed recording is performed by using the information-recordingmedium wherein the information α concerning the relationship among thevalue Pb1 which is larger than Pr and smaller than Pb, the value Pb2which is larger than Pb and smaller than Pp, and Pb is recorded, it ispossible to improve the archival overwrite characteristic foroverwriting information after storing the medium for a certain period oftime in the high temperature environment by setting α to have theappropriate value depending on the recording speed.

[0090] In the embodiment described above, the data is recorded on theland. However, the same or equivalent effect is obtained even when therecording is performed on the groove. In the embodiment of the presentinvention, the radial position of the recording is not specificallydescribed. However, the same or equivalent effect is obtained at anarbitrary radius of 24 to 58 mm. In the embodiment of the presentinvention, the signal is reproduced at the linear velocity of 8.2 m/sec.However, the essential characteristic of the present invention is in theimprovement in the high speed recording process. Therefore, the effectof the present invention can be obtained especially regardless of thespeed or velocity of the reproduction.

[0091] The characteristic of the present invention is in the recordingof the information in relation to the definition of the erasing power onthe information-recording medium together with the information on therecording velocity in order to improve the archival overwritecharacteristics in accordance with the realization of the high speedrecording. The effect of the present invention can be obtainedirrelevant to the structure or construction of the information-recordingmedium, the composition, the crystallization speed, the crystallizationtemperature, the crystal nucleus-generating temperature, and the meltingpoint.

[0092] In the embodiment of the present invention, the threshold valueis 13% in order to determine the values of Pb1 and Pb2 from thedependency of the erasing power on the jitter. However, the essentialcharacteristic of the present invention is not affected by the thresholdvalue of the jitter. The effect of the present invention is not losteven when an arbitrary threshold value is used to determine the valuesof Pb1 and Pb2, for example, from the dependency of the erasing power onthe error rate and/or the dependency on the signal amplitude, S/N, orthe asymmetry without using the jitter when the values of Pb1 and Pb2are determined.

[0093] In this specification, the light beam for the recording isexpressed as “laser beam”. However, as for the present invention, theeffect of the present invention is obtained with any energy beamprovided that the energy beam is capable of changing the state of theinformation-recording portion of the information-recording medium.Therefore, the effect of the present invention is not lost even when theenergy beam such as an electron beam is used.

[0094] In the embodiment of the present invention, the red laser havingthe wavelength of 655 nm is used. However, the present invention is notespecially affected by the wavelength of the laser. The effect isexhibited even in the case of any information-recording apparatus whichuses a laser having a relatively short wavelength such as the blue laserand the ultraviolet laser and any information-recording medium used forsuch an information-recording apparatus.

[0095] In the embodiment of the present invention, the phase-change diskis used for the information-recording medium. However, the presentinvention is applicable to any information-recording medium providedthat information is recorded on the information-recording medium bybeing irradiated with an energy beam. Therefore, the present inventionis not especially affected by the material and the structure forconstructing the information-recording medium and the shape of theinformation-recording medium. The present invention is also applicableto information-recording media such as optical cards other than thedisk-shaped information-recording medium.

[0096] According to the information-recording method, theinformation-recording medium, and the information-recording apparatus ofthe present invention, it is possible to improve the overwritecharacteristic in the high speed recording, especially the archivaloverwrite characteristic for overwriting information after retaining themedium in a high temperature environment for a certain period of time.Therefore, the present invention makes it possible to further improvethe reliability of the large capacity high speed data recordingirrelevant to the surrounding environment.

What is claimed is:
 1. An information-recording method for recordinginformation on an information-recording medium by radiating a light beampower-modulated to be at a recording power level and an erasing powerlevel, the information-recording method comprising: overwriting a randompattern on the information-recording medium with light beams having apredetermined recording power and a variety of erasing powers;reproducing the overwritten random pattern to determine a minimum valuePb1 and a maximum value Pb2 of the erasing power obtained when thepattern, in which a reproduction jitter or a reproduction error exceedsa predetermined threshold value, is erased; determining an optimumerasing power Pb for performing the recording from the determinedminimum value Pb1, the determined maximum value Pb2, and a relationalexpression represented by Pb=α×Pb1+(1−α)×Pb2; and recording theinformation with the determined optimum erasing power Pb.
 2. Theinformation-recording method according to claim 1, further comprisingdetermining an optimum recording power Pp by using the determinedoptimum erasing power Pb.
 3. The information-recording method accordingto claim 1, wherein α differs within a range of α≦0.50 depending on arecording speed when the information is recorded at different recordingspeeds.
 4. The information-recording method according to claim 1,wherein a value of α is previously recorded on the information-recordingmedium, and the value of α is read from the information-recording mediumwhen the information is recorded.
 5. The information-recording methodaccording to claim 2, wherein Pr<Pb1<Pb and Pb<Pb2<Pp are satisfiedprovided that a reproducing power is Pr.
 6. An information-recordingmedium for recording and reproducing information thereon, theinformation-recording medium comprising: an information-recordingportion on which the information is recorded by being irradiated with alight beam having a recording power Pp and an erasing power Pb lowerthan the recording power Pp and on which the information is reproducedby being irradiated with a light beam having a reproducing power Prlower than the erasing power Pb; and a control data portion, wherein:information for determining an optimum erasing power Pb from a minimumerasing power Pb1 which satisfies Pr<Pb1<Pb and a maximum erasing powerPb2 which satisfies Pb<Pb2<Pp is previously recorded on the control dataportion.
 7. The information-recording medium according to claim 6,wherein the information for determining the optimum erasing power Pbfrom Pb1 and Pb2 is recorded together with information which relates toa recording speed.
 8. The information-recording medium according toclaim 6, wherein the information for determining the optimum erasingpower Pb from Pb1 and Pb2 is α which is represented by an expression ofPb=α×Pb1+(1−α)×Pb2.
 9. The information-recording medium according toclaim 8, wherein a value of α satisfies α≦0.50.
 10. Theinformation-recording medium according to claim 9, wherein the value ofα satisfies 0.25≦α≦0.50.
 11. The information-recording medium accordingto claim 6, wherein a linear velocity, which is used when theinformation-recording medium is moved relative to the light beam forrecording the information, is not less than 9 m/sec.
 12. Aninformation-recording apparatus for recording information on aninformation-recording medium by radiating a light beam power-modulatedto be at a recording power level and an erasing power level, theinformation-recording apparatus comprising: an optical head whichradiates the light beam onto the information-recording medium; a driverwhich drives the optical head so that the light beam, which ispower-modulated to be at the recording power level and the erasing powerlevel, is outputted from the optical head; and a Pb-calculating controlunit which reproduces a random pattern overwritten with light beamshaving a predetermined recording power and a variety of erasing powersto determine a minimum value Pb1 and a maximum value Pb2 of the erasingpower obtained when the pattern with a reproduction jitter or areproduction error exceeding a predetermined threshold value is erased,which reads a coefficient α which is used in an expressionPb=α×Pb1+(1−α)×Pb2 and has been previously recorded on theinformation-recording medium, and which determines an optimum erasingpower Pb to be used when the recording is performed, from the determinedminimum value Pb1, the determined maximum value Pb2, and the readcoefficient α.